1. Field of the Invention
The present invention relates to a method for preventing clogging of a urea injection nozzle of a SCR system. More particularly, the present invention relates to a method for preventing clogging of a urea injection nozzle of an SCR system which determines pressure within a supply module and prevents clogging of the urea injection nozzle in an after-run operation.
2. Description of Related Art
Generally, exhaust gas exhausted from an exhaust manifold of an engine is guided to a catalytic converter mounted in an exhaust pipe and purified, passes through a muffler to reduce noise, and is finally exhausted through the exhaust pipe to atmosphere.
The catalytic converter treats pollutants such as NOx within the exhaust gas.
A selective catalytic reduction (SCR) apparatus, one of catalytic converters, purifies NOx within the exhaust gas, and urea, ammonia, carbon monoxide, hydrocarbon (HC), and so on are used as a reductant.
When the reductant is supplied to the exhaust gas, nitrogen oxide within the exhaust gas is deoxidized to nitrogen by an oxidation-reduction reaction with the reductant.
FIG. 1 is a drawing showing a conventional SCR system.
As shown in FIG. 1, the conventional SCR system includes a urea tank 60 in which urea 62 is stored, a supply module 50 supplying the urea 62 from the urea tank 60, and a urea injection nozzle 20 supplying the urea supplied by the supply module 50 to a selective catalytic reduction catalyst 12.
The urea 62 passes through a filter 52 and is supplied an exhaust pipe 10 in front of the SCR catalyst 12.
A dosing control unit (DCU) 25 controls a supply amount of the urea 62.
A temperature sensor 15 may detect a temperature of the urea 62 or detect temperature of the exhaust gas passed through the SCR catalyst 12.
The urea 62 has characteristics that it is frozen at −11° C. or less and corrosiveness thereof is increased at 70° C. or more. Therefore, the urea 62 is withdrawn to the urea tank 60 when a vehicle and a system stop, which is called “after-run”.
While the SCR apparatus is operated, the urea 62 is supplied from the urea tank 60 and the supply module 50 to the urea injection nozzle 20, and in the after-run operation, the urea is withdrawn in a reverse order.
If the urea injection nozzle 20 is heated by exhaust gas, the temperature of the urea reaches a crystallization temperature (71-75° C.), and as the after-run is operated with the urea injection nozzle 20 100% open, crystallization of the urea is generated in the urea injection nozzle 20 and thus the urea injection nozzle may be clogged.
That is, while the after-run is operated, the urea injection nozzle 20 has to be opened, and crystallization of the urea is generated in the urea injection nozzle 20, however clogging of the urea injection nozzle 20 may not be detected.
Particularly, if backward flow of the urea 62 from the urea tank 60 to the supply module 50 occurs in the winter season, the SCR system may be damaged.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.